The present invention relates to three-axis positioning jacks, capable of supporting objects whose weights can be as high as several hundred metric tons whilst allowing their positioning with an accuracy of the order of one micrometer.
At present, when a structure has to be positioned or shaped with respect to a foundation, jacks are used which are disposed between that foundation and the structure. These jacks are adjusted manually or electrically by agents who will carry out iterative adjustment operations until the desired position is reached. It is however extremely difficult in practice, if not impossible, to obtain high accuracy in such a context.
For the positioning of these structures, the actuators normally used are jacks, the two best known types of which are:
mechanical jacks, PA1 hydraulic jacks. PA1 the equipment is often dirty, the fluid-tightness of the hydraulic chambers becoming relative because of the wear and ageing of the seals; PA1 micrometric positioning is impossible, the slight leakages and the high coefficient of expansion of the liquids used give rise to this positioning inability; PA1 the manufacturing cost is generally high, the friction surfaces necessitating precise and high-quality practices. PA1 a base comprising movable supporting means and means for vertically displaying said movable supporting means, and PA1 a rod providing a link between the movable head of said jack and said base. PA1 a base comprising a bore containing a chamber in which there is confined a working fluid and a rod providing a link between the head of the jack and the base, PA1 and means for modifying the shape of the confinement chamber for the purpose of obtaining a vertical displacement of the head, these means comprising at least one motorised actuating piston, characterized in that the working fluid is constituted by the elastomer mass. PA1 a three-axis positioning jack, two of the axes being motorised, one of them being vertical and the other planimetric, the remaining axis being free or guided; PA1 a three-axis positioning jack having a vertical motorised axis, the other two planimetric axes being free or guided. PA1 additional actuating pistons can be distributed over the periphery of the chamber in order to increase or pre-adjust the travel of the jack; these actuating pistons are then driven by a screw-nut system which can be motorised or hand-driven; PA1 a mechanical system for pre-loading (by springs) the elastomer can be provided for use under very light loads; PA1 a displacement sensor can be associated with the jack for the servo-controlled versions.
The mechanical solution, which is the most conventional one, uses a micrometric ball screw driven by a stepper motor. A compensation system often relieves the screw for heavy load applications. The principle of the hydraulic jack is itself so well known and its use is so widespread that a description of this type of jack would be superfluous if our new jack did not exhibit similarities with this technology.
In a hydraulic jack, a piston, provided with a fluid-tight seal, is free to move in the base of the jack, whose chamber is filled completely with a liquid which is only very slightly compressible. The piston moves, either because the volume of liquid in the chamber is modified by the injection or evacuation of the liquid via a pipe, a pump, a stop valve and a reservoir, or because an actuating piston, which is also provided with a fluid-tight seal, driven for example by a screw/nut assembly, modifies the shape of the chamber. As the liquid is virtually incompressible, the piston moves such that the volume of the chamber remains practically constant.
However, this type of jack which makes it possible to apply very high forces has three disadvantages:
From the French patent FR 2179572 there is known a force multiplier device comprising a first hydraulic jack, whose piston rod is mounted slidingly in an enclosure integral with the base of that jack and constituting the chamber of a second jack also equipped with a sliding piston subjected to the action of an elastomer confined in that chamber and transmitting pressures in a hydrostatic manner.
There is also known, from the German patent DE 3916539, a transmission and/or pressure device comprising a principal piston driven by a rod subjected to a pressure. This piston acts on an elastomer mass confined in a chamber and which provides transmission of pressure to two actuating pistons. These actuating pistons are controlled in displacement by piezoelectric actuators.
These force multiplier devices use an elastomer mass as a working fluid. They cannot however provide the function of a positioning jack offering the accuracy required here. In fact, in the device described in the document FR 2179572, the first jack or actuating jack is a hydraulic jack, which makes it difficult to attempt to achieve high accuracy. Furthermore, the transmission device divulged in the document DE 3916539 is not a force multiplier and cannot be used as a positioning jack since its principal piston has a cross-section less than that of the actuating pistons controlled by the piezoelectric actuators and small travels are therefore obtained at the level of the actuating pistons and a large travel of the principal piston is obtained, which would not make it possible to obtain the required level of accuracy.
The purpose of the present invention is to overcome these disadvantages by proposing a three-axis positioning jack which procures a high positioning accuracy whilst being of less expensive and more reliable construction than those of jacks of the prior art.
This purpose is reached with a three-axis positioning jack with at least one motorised axis, comprising:
According to the invention, the linking rod is designed to form a double connection of the ball joint type providing with a lateral displacement of the head with respect to the base, and the movable supporting means comprise an elastomer mass on which the lower end of the linking rod is supported.
Such a jack allows, by means of the double link of the ball joint type, a more accurate tridimensional positioning than what can be expected from present jack techniques. Implementing a piece made with an elastomer material procures effort transmission and damping functions that are particularly appreciated in position controls for heavy structures.
Moreover, in a first embodiment of jacks according to the invention, the piece made from an elastomer material can be advantageously used as a working fluid.
Thus, there is proposed a three-axis positioning jack having at least one motorised axis, comprising:
In this first embodiment, the solid elastomer mass, which behaves like a quasi-fluid when under load, is deformed by an actuating piston which is motorised. This deformation has the effect of displacing the working piston in order that the volume of the chamber remains constant. The servo-control of a one-axis motorised jack according to the invention with respect to an absolute reference allows easy use of the latter in installations requiring an alignment of deformable structures. Furthermore, one-axis jacks according to the invention can be designed such that they are extra-flat.
The condition for correct operation of this new type of jack is that the pressure generated by the load applied to the piston which compresses the elastomer must be sufficient for the latter to behave like a quasi-fluid without, however, its viscosity lowering to such an extent that the polymer can be extruded through the construction clearance between the piston and the bore made in the base of the jack. This jack has minimum and maximum loads proportional to the cross-section of the bore-piston pair and to the Shore hardness of the elastomer used.
In a second embodiment of the present invention, there is proposed a three-axis positioning jack, characterised in that the movable supporting means comprise a movable piece for receiving the elastomer piece acting as a ball joint, said movable piece being slidingly mounted with respect to the base and being actuated by micrometric ball screw means.
This jack further comprises preferably a second elastomer piece acting as a ball joint between the higher end of the connecting rod and the movable head.
A bone-shaped connecting rod with complex-shaped ends can be provided, with said elastomer pieces preferably having housings or hollows fitted for receiving the respective ends of the connecting rod. Cylinder-shaped elastomer pellets can also be used with plane supporting faces against which plane or substantially plane ends of a connecting rod are supported.
Jacks according to the invention are compact and of small size. Furthermore, they are easy to produce and are therefore economical. Their functioning is reliable since there is no longer any risk of a sealing breakdown. Furthermore, coupled with servo-control means, jacks according to the invention allow very accurate positioning because of a high positioning resolution.
In this way there are available, with three-axis positioning jacks according to the invention, particularly effective actuators for carrying out positioning of a heavy structure with respect to an absolute reference or of several structures with respect to each other, with a high level of accuracy, since by combining several three-axis jacks according to the invention (for example three three-axis jacks of which two axes are motorised), it is possible to control the six degrees of freedom of an object.
Within the framework of the present invention, it is possible to provide:
A three-axis positioning jack of which two axes are motorised can furthermore comprise a motorised stop to procure a lateral displacement of the head of the jack along a first horizontal axis. This motorised stop comprises for example an actuating screw driven by a motor reduction gear.
Furthermore, in order to achieve manual guidance or displacement of the head of the jack along the non-motorised horizontal axis, it is possible to provide a screw and its thrust ring for this purpose.
Three-axis positioning jacks according to the invention can advantageously be servo-controlled in position with respect to an absolute reference, along at least one of the said motorised axes.
According to particular embodiments of one or three-axis jacks according to the invention,
Displacement sensors can be associated with all of these embodiments, allowing a relative servo-control of these jacks.
According to yet another aspect of the invention, there is proposed a method for the servo-control of the position of a structure supported by positioning jacks according to the invention, comprising measurements of the position of this structure and with each jack being servo-controlled on the basis of these measurements and of position commands.
Advantageously, it is possible to use a set of N jacks with one servo-controlled axis, to act on a deformable solid and to define its geometry, for example for the servo-levelling or servo-alignment of large machines or of long tubes, or for correcting the shape of a deformable solid of large size, or for achieving the flatness of a frame of a large machine tool or the straightness of the movement of translation of a large mass.
Servo-controls of N jacks according to the invention using the appropriate number of sensors measuring with respect to one or more absolute references are also included within the scope of the present invention.
Other features and advantages of the invention will furthermore appear in the following description. In the accompanying drawings given by way of non-limitative examples: